IR STUDIES ON CO INSERTION REACTION WITH SIO2-SUPPORTED RHODIUM ACTIVE-SITE

The reactions of Rh-0-coordinated CO and Rh-0-adsorbed CO with C2H4 H-2 at 293 K were monitored by IR spectroscopy. The linear CO adsorbed on Rh-0/SiO2 is consumed with formation of propanal whereas the coord inated CO in Rh-6(CO)(16)/SiO2 and its derivative do not participate i n CO insertion. IR study of the thermal decomposition of Rh-6(CO)(16)/ SiO2 indicates that the cluster can be stabilized on the surface up to 548 K by gaseous CO under hydroformylation conditions. Moreover the R h-6(CO)(16)/SiO2 system exhibits increased catalytic hydroformylation activity with reducing coordinated CO. These results show that coordin ative unsaturation on the Rh-0 surface is necessary for heterogeneousl y rhodium-catalyzed hydroformylation and that totally decarbonylated R h-0/SiO2 is most effective.